Use of an adjustable expansion vavle to control dehumidification

ABSTRACT

A refrigerant system is provided with a control for its expansion device. The control operates the expansion device to adjust the superheat of the refrigerant leaving an evaporator to have desired dehumidification for air being delivered into an environment to be conditioned.

BACKGROUND OF THE INVENTION

This application relates to a refrigerant system incorporating anadjustable expansion valve, and more particularly, to a refrigerantsystem wherein this adjustable expansion valve is controlled to achievedesired dehumidification within a climate-controlled environment. Atypical example of such an adjustable expansion device is an electronicexpansion valve.

Refrigerant systems are known in the HVAC&R (heating, ventilation, airconditioning and refrigeration) art, and operate to compress andcirculate a refrigerant throughout a closed-loop refrigerant circuit,connecting a plurality of components, to condition a secondary fluid tobe delivered to a climate-controlled space. In a basic refrigerantsystem, refrigerant is compressed in a compressor from a lower to ahigher pressure and delivered to a heat rejection heat exchanger(condenser or gas cooler). From the heat rejection heat exchanger, whereheat is typically transferred from the refrigerant to an ambientenvironment, a high-pressure refrigerant flows to an expansion devicewhere it is expanded to a lower pressure and temperature and then isrouted to a heat accepting heat exchanger (evaporator), whererefrigerant cools a secondary fluid to be delivered to the conditionedenvironment. From the evaporator, refrigerant is returned to thecompressor. One common example of refrigerant systems is an airconditioning system, which operates to condition (cool and oftendehumidify) air to be delivered into a climate-controlled zone or space.

Refrigerant systems are utilized to provide temperature control, andoften humidity control, for air supplied into an occupied environment.One feature that is important to the reliable and efficient operation ofa refrigerant system is the amount of superheat of the refrigerantleaving the evaporator and moving to the compressor. Typically, thesuperheat, which is defined as a difference between the actualtemperature and the saturation temperature of the refrigerant, must bekept within a tight band for most efficient and reliable operation ofthe refrigerant system. Moreover, it is also typical that for puretemperature control, a refrigerant system operates most efficiently withthe lowest safe superheat amount that can be accurately sensed andmaintained over a wide range of environmental and operating conditions.For various reasons, the superheat needs to be kept several degreesabove zero, and it is typically maintained in the low range from 6 to12° F.

Control of the evaporator superheat has been provided for a variety offunctions, however, the evaporator superheat has not been controlled tocontrol dehumidification of the air being delivered into an environmentto be conditioned.

SUMMARY OF THE INVENTION

In a disclosed embodiment of this invention, a control for an electronicexpansion valve (EXV) achieves a desired refrigerant superheat at theevaporator exit such that the dehumidification provided by therefrigerant system to the air delivered into a conditioned environmentcan be controlled. In one embodiment, the “dehumidification” mode ofsuperheat control is only entered if a reduced cooling load provided bythe refrigerant system is desired. In another embodiment, variousconditions for reliable operation of the refrigerant system, such asdischarge temperature and saturation suction temperature being withinspecified respective ranges, have to be satisfied while entering intothe “dehumidification” mode of superheat control or continuouslyoperating in the “dehumidification” mode of superheat control.

These and other features of the present invention can be best understoodfrom the following specification and drawings, the following of which isa brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of the basic refrigerant system incorporatingthe present invention.

FIG. 2 is an example of simplified flowchart of one embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a refrigerant system 20 incorporating a compressor 22 forcompressing a refrigerant and delivering it downstream to a heatrejection heat exchanger 24. From the heat rejection heat exchanger 24,the refrigerant passes through an electronic expansion valve 26, andthen to an evaporator 30. As shown, air moving over the evaporator 30 isdelivered into an environment to be conditioned 32. The environment tobe conditioned 32 is provided with a control 43 that allows an occupantto select desired temperature and/or humidity levels to be provided bythe air being delivered into the environment.

A control 28 is shown for the electronic expansion device 26. Moreover,transducers or other sensors 34 and 36 are shown in various locationswithin the refrigerant system 20. As shown, a transducer 34 is provideddownstream of the compressor and may sense the pressure and/ortemperature at the discharge of the compressor 22. Similarly, a sensor36 may sense the pressure and/or temperature downstream of theevaporator 30. The sensors 34 and 36 signals are provided to the control28. It should be noted that some of these sensors are optional and maynot be required for certain system configurations.

Controls are known which operate to control electronic expansion devicesto achieve desired superheat values downstream of the evaporator 30.Typically, to achieve desirable performance (total capacity andefficiency) for the refrigerant system 20 while preserving reliabilityof the compressor 22, it would be desirable to control the evaporatorsuperheat to low positive values, typically in the range from 6 to 12°F.

In this invention, however, the inventors have recognized that byincreasing superheat under certain circumstances, could lead toincreased dehumidification capability of the evaporator 30 and in turnlower humidity of the air being delivered into the conditionedenvironment 32. Thus, the present invention utilizes its control of theexpansion device 26 to achieve increased dehumidification, at leastunder certain circumstances.

It should be noted that total capacity of the evaporator 30 decreaseswhen superheat is increased, while a simultaneous capacity shift fromthe sensible component to the latent component is taking place. As aresult, a sensible heat ratio (the ratio of the sensible capacity to thetotal capacity) provided by the evaporator 30 is reduced. Therefore, byincreasing evaporator superheat, operation of the refrigerant system 20can be focused more on providing dehumidification, if desired, whilefull cooling sensible capacity is not required. In other words, thesensible heat ratio of the evaporator 30 can be controlled bycontrolling the electronic expansion valve 26 and consequently adjustingsuperheat at the exit of the evaporator 30. Therefore, by controllingthe electronic expansion valve 26, the total evaporator capacity as wellits sensible and latent components can be controlled.

Feedback from the sensors 34 and 36 may be used to ensure that theincreased superheat is provided to ensure desired dehumidificationwhile, at the same time, any unreliable or unsafe operational limits arenot being approached. For instance, the desired superheat range may bedefined by a lower limit and a higher limit, with the lower limitrestricted by a minimum value of the evaporator pressure (or saturationtemperature) and the higher limit constrained by a discharge temperaturethreshold. As known, abnormally low evaporator pressure may cause theevaporator freeze-up and excessively high discharge temperature may leadto the compressor damage.

As shown in FIG. 2, the control 28 may normally operate to achieve adesired optimal superheat in a conventional cooling mode, for instance,to provide maximum performance (capacity and efficiency) for therefrigerant system 20 to cool the air delivered to the conditionedenvironment 32. However, at least under circumstances where a reducedsensible cooling load is demanded, such as, for instance, when theambient temperature is sufficiently low or/and sensible cooling loaddemands in the conditioned space 32 are not significant, the control 28enters a “dehumidification” mode of superheat control. In this“dehumidification” mode, the control 28 may control the expansion device26, such that superheat is adjusted so that the capacity of theevaporator 30 is shifted from cooling to dehumidification (to lowersensible heat ratios) to reduce humidity of the air being delivered intothe zone to be conditioned 32. A worker of ordinary skill in the artwould recognize how to control the electronic expansion device 26, giventhe goals of this application as described above, including maintainingthe operation of the refrigerant system 20 within safety and reliabilitylimits.

It should be noted that superheat control may be executed at thecompressor suction or compressor discharge. In case of the compressorsuction, it can be executed at the location toward the compressorsuction instead of the evaporator exit. Further, superheat control canbe executed at the compressor discharge, if the relationship betweensuction superheat and discharge superheat is known. Further, even undercircumstances when the desired humidity level cannot be preciselyachieved by the evaporator superheat control, it still can be noticeablyreduced towards the desired value providing a higher degree of comfortfor an occupant of the conditioned space.

It should be pointed out that many different compressor types could beused in this invention. For example, scroll, screw, rotary, orreciprocating compressors can be employed. The refrigerant systems thatutilize this invention can be used in many different applications,including, but not limited to, stationary and mobile air conditioningsystems as well as heat pump systems. The refrigerant system can alsoemploy vapor injection, liquid injection, multiple circuits, as well ascompressors connected in parallel in a tandem fashion.

Although embodiments of this invention have been disclosed a worker ofordinary skill in the art would recognize that certain modificationswould come within the scope of this invention. For that reason thefollowing claims should be studied to determine the true scope andcontent of this invention.

1. A refrigerant system including: a compressor for compressing arefrigerant and delivering it downstream into a heat rejection heatexchanger, the refrigerant from said heat rejection heat exchangerpassing through an adjustable expansion device, and then through anevaporator, before being returned to the compressor; and a control forsaid adjustable expansion device, said control being operable to controldehumidification in an environment to be conditioned by controlling saidadjustable expansion device.
 2. The refrigerant system as set forth inclaim 1, wherein said dehumidification control consists of changingrefrigerant superheat.
 3. The refrigerant system as set forth in claim2, wherein said superheat is at least one of suction superheat anddischarge superheat.
 4. The refrigerant system as set forth in claim 1,wherein said dehumidification control has a limit on the maximumacceptable superheat.
 5. The refrigerant system as set forth in claim 1,wherein said adjustable expansion device is an electronic expansionvalve.
 6. The refrigerant system as set forth in claim 1, wherein saidcontrol being provided with feedback of at least one measurement withinsaid refrigerant system.
 7. The refrigerant system as set forth in claim6, wherein said feedback includes feedback from at least one of thepressure and temperature measurement at the discharge of saidcompressor.
 8. The refrigerant system as set forth in claim 6, whereinsaid feedback includes feedback from at least one of the pressure andtemperature measurement in at least one location selected from thefollowing locations: the evaporator, the compressor or between theevaporator and the compressor.
 9. The refrigerant system as set forth inclaim 1, wherein said control has a dehumidification mode at which itincreases the superheat of the refrigerant leaving the evaporator, whenfull sensible cooling capacity of the refrigerant system is notrequired, to provide desired dehumidification.
 10. The refrigerantsystem as set forth in claim 1, wherein said control has adehumidification mode at which it increases the superheat of therefrigerant leaving the evaporator, when full sensible cooling capacityof the refrigerant system is not required, to provide the desiredsensible heat ratio.
 11. The refrigerant system as set forth in claim 1,wherein said control has a dehumidification mode at which it increasesthe superheat of the refrigerant leaving the evaporator, when fullsensible cooling capacity of the refrigerant system is not required, toprovide the desired latent capacity and the desired sensible capacity.12. A method of operating a refrigerant system including the steps of:(a) compressing a refrigerant and delivering it downstream into a heatrejection heat exchanger, the refrigerant from said heat rejection heatexchanger passing through an adjustable expansion device, and thenthrough an evaporator, before being returned to the compressor; and (b)controlling said adjustable expansion device to control dehumidificationin an environment to be conditioned by controlling said adjustableexpansion device.
 13. The method as set forth in claim 12, wherein saidcontrol being provided with feedback of at least one measurement withinsaid refrigerant system.
 14. The method as set forth in claim 13,wherein said feedback includes feedback from at least one of thepressure and temperature measurement at the discharge of saidcompressor.
 15. The method as set forth in claim 13, wherein saidfeedback includes feedback from at least one of the pressure andtemperature measurement in at least one location selected from thefollowing locations: the evaporator, the compressor or between theevaporator and the compressor.
 16. The method as set forth in claim 12,wherein said control moving into a dehumidification mode at which itincreases the superheat of the refrigerant leaving the evaporator, whenfull sensible cooling capacity of the refrigerant system is notrequired, to provide desired dehumidification.
 17. The method as setforth in claim 12, wherein said control moving into a dehumidificationmode at which it increases the superheat of the refrigerant leaving theevaporator, when full sensible cooling capacity of the refrigerantsystem is not required, to provide the desired sensible heat ratio. 18.The method as set forth in claim 12, wherein said control moving into adehumidification mode at which it increases the superheat of therefrigerant leaving the evaporator, when full sensible cooling capacityof the refrigerant system is not required, to provide the desired latentcapacity and the desired sensible capacity.
 19. The method as set forthin claim 12, wherein said dehumidification control consists of changingrefrigerant superheat.
 20. The method as set forth in claim 13, whereinsaid superheat is at least one of suction superheat and dischargesuperheat.
 21. (canceled)
 22. (canceled)